This invention relates to an automated storage and retrieval system and more particularly to a structure for a vehicle and the track on which such vehicle rides suitable for use in such a system.
Automated storage and retrieval systems of the type presently known in the art are generally rack structures which include a plurality of lanes and a number of aisles which extend orthogonally form each lane. Items being stored in the rack, such as loaded pallets, are positioned in the aisles. To retrieve a loaded pallet from a position within an aisle or to deposit a loaded pallet therein, it is necessary for a vehicle, commonly referred to as a satellite vehicle, to enter the aisle. These aisles are formed by pairs of horizontal rails, which rails function as tracks for the satellite vehicles.
The use of such automated storage and retrieval systems including such automated satellite vehicles has contributed greatly to the efficiency and economy of modern warehousing. However, as such satellite vehicles are called upon to carry larger, that is, heavier loads, it has become necessary to increase the structural strength of the rack structure, part of which functions as the rails upon which such satellite vehicles travel. With such warehouses now reaching heights in the area of 100 feet and containing tens of thousands of pallet positions, each increase required in the structural strength of the rack means many additional tons of steel being used to fabricate the rack structure and thus, in turn, results in substantially increased costs. Clearly, constantly increasing rack strength to accommodate the ever-increasing loads stored and moved within the racks results in constantly increasing the cost of fabricating and operating a system which was originally conceived as one which would decrease costs.
A number of structural concepts have been developed in an attempt to provide a solution to the aforementioned problem. For example, larger wheels have been provided for the satellite vehicles in an effort to enable them to carry the heavier loads. However, the provision of relatively large wheels on vehicles which usually have a mimimum of eight wheels per vehicle (four on each side arranged in pairs with one pair at the front end and one pair at the aft end of the vehicle), has greatly added to the cost of such vehicles. Another potential solution which has been developed has been to coat the vehicle wheels with a deformable material, such as, for example, a urethane, thereby insuring that each wheel will have a larger footprint, thus enabling it to support a greater portion of the vehicle load without increasing wheel size. None of these solutions, however, has proved to be completely satisfactory. This is due, at least in part, to the fact that unless the rack structure itself is made substantially more rigid, it deflects longitudinally, thereby causing a major portion, if not all, of the load weight to be supported solely by the outer wheels (i.e., the forward and aft wheels of each pair) of the vehicle without assistance, or with only minimal assistance, from the interior vehicle wheels.